The present invention is generally directed to toner compositions, and more specifically to encapsulated colored heat fusible toner compositions. In one embodiment, the present invention is related to encapsulated toner compositions comprised of a core with a polymeric shell thereover preferably prepared by interfacial polymerization. Another specific embodiment of the present invention relates to encapsulated toner compositions comprised of a core containing a preformed polymer and/or monomer or monomers, a free radical initiator, pigment or dye particles and wherein the core which is dispersed into an emulsifier solution is subsequently encapsulated by a polymeric shell, and wherein the toner is stabilized by dispersants at elevated temperatures during core polymerization via free radical polymerization.
Toners suitable for use in electrophotographic copiers and printers may include therein a wide variety of colors, such as black, red, green, blue, brown, yellow, purple, silver and gold. When it is desired to highlight certain features of a document, one or more colored toners are typically used in conjunction with a black toner to provide an image in two or more colors. Full color images can also be generated by developing images with cyan, magenta, yellow and black toners. Generally, it is advantageous for such toners to exhibit low melting temperatures to enable low energy fusing of the developed images to substrates at lower temperatures and lower pressures of, for example, 400 psi versus, for example, about 4,000 psi for cold pressure fixable applications. It is also often advantageous for such toners to possess mean particle diameters of from about 5 microns to about 35 microns and preferably from about 5 microns to about 15 microns to enable images of high resolution, low image noise and high color fidelity. Further, it is generally desirable for these small diameter toners to have very narrow size distributions, preferably with a GSD (Geometric Standard Deviation) of 1.5 or less, to avoid difficulties in the electrophotographic development and transfer associated with oversize toner particles and extremely fine toner particles. These and other advantages can be achieved with the encapsulated toners and processes of the present invention. More specifically, an advantage associated with toner particles of the present invention is the enablement of the stabilization of toner particles at elevated temperatures during core monomer polymerization by the addition of dispersing components including those available as Daxad.TM. from W. R. Grace Chemical Company. The aforementioned stabilization enables the utilization of less emulsifier for the toner particle generation step, and therefore the emulsifiers primary function is to control the particle size of the toner generated during the dispersion of the organic phase into the aqueous phase, and moreover the dispersing agents can be selected for stabilization of the toner particles. Further, reducing the quantity of emulsifier selected results in the generation of less fine particles with an average particle diameter of less than about 1 micron thereby enabling, for example, toner particles with clean surfaces. Additionally, with the toner particles and processes of the present invention there is eliminated or minimized undesirable particle agglomeration, especially at elevated temperatures, and furthermore by the incorporation of certain dispersants there is permitted toner particles with heat fusible cores (Tg less than 55.degree. C.) and heat fusible shells with a Tg of, for example, less than 100.degree. C., which particles remain as discrete primary particles subsequent to the free radical polymerization. The addition of dispersants prior to core monomer polymerization when emulsifiers such as polyvinyl alcohol are utilized enable a reduction of grafting or shell incorporation of such emulsifier on the toner particle surface primarily, it is believed, since a minimum amount of emulsifier is needed to generate the desired particle size. By reducing the grafting of the emulsifier such as polyvinyl alcohol, onto or into the shell there is enabled lower heat fusible toners since the thermal properties of the shell are usually not increased. Also, it is advantageous to add the dispersants illustrated herein to the toner synthesis in some embodiments prior to free radical polymerization particularly since its stabilization capabilities permits increased loading of the organic phase into the aqueous phase thereby allowing increased toner throughput. The addition of dispersing agent prior to core polymerization can also desirably influence the triboelectric charging properties of the toner, and can, in some instances, function as a negative charge control additive. Further, the incorporation of the aforementioned dispersants as charge control additives during interfacial polymerization reduces the number of process steps and moreover the dispersant can be incorporated into the shell in some embodiments but may not strengthen or reinforce the shell as in the situation with poly(vinyl alcohol). Also, in some embodiments the dispersants selected for the toners and processes of the present invention do not increase the fusing temperatures of the toner or only cause minimum increases in the aforementioned temperatures.
The toner compositions of the present invention can be selected for a variety of known imaging and printing processes including electrophotographic, electrographic or magnetographic processes. Specifically, the toner compositions of the present invention can be selected for xerographic imaging and printing processes, such as two component development systems and single component development systems both magnetic and nonmagnetic along with ionographic processes wherein dielectric receivers such as silicon carbide are utilized, reference U.S. Pat. No. 4,885,220 entitled Amorphous Silicon Carbide Electroreceptors, the disclosure of which is totally incorporated herein by reference.
In a patentability search report, there were recited as prior art the following U.S. Pat. No. 4,727,101, the disclosure of which is totally incorporated herein by reference, which illustrates a free radical polymerization of a toner shell at elevated temperatures and more specifically is directed to the preparation of encapsulated toner compositions, which comprises mixing in the absence of a solvent a core monomer initiator, pigment particles, a first shell monomer, stabilizer, and water, and thereafter adding a second shell monomer to enable interfacial polymerization interaction, and subsequently affecting the free radical polymerization of the core monomer, reference the Abstract of the Disclosure for example; U.S. Pat. No. 4,777,104 which relates to processes for the formation of electrophotographic toners of certain desired sizes by radical polymerization, reference for example column 3, lines 26 to 41, and also note the disclosure in column 6 with respect to colorants beginning at line 29; U.S. Pat. No. 4,524,199, the disclosure of which is totally incorporated herein by reference, which relates to stable polymeric dispersions, which dispersion comprises, for example, a polar dispersion medium having dispersed therein particles comprising a thermoplastic resin core having irreversibly anchored thereto a nonionic amphipatic steric stabilizer comprising a graph copolymer, reference for example column 2, beginning at line 45, and note column 4, beginning at line 57, and continuing on to column 5; U.S. Pat. No. 4,533,617 directed to heat fixable developers with a capsule structure containing a binder resin of a certain glass transition temperature and a colorant coated with a vinyl type polymer, reference for example the Abstract of the Disclosure, and note columns 4 through 10; U.S. Pat. No. 4,725,522 directed to processes for cold pressure fixable encapsulated toner compositions, particularly processes thereof wherein a water phase containing a stabilizing material is selected and hydrolysis is accomplished by heating and there is utilized interfacial polymerization to form the shell, reference for example the Abstract of the Disclosure, and also note columns 4 to 8, the disclosure of the aforementioned patent being totally incorporated herein by reference; U.S. Pat. No. 3,876,610 relating to the preparation of electrostatic toner materials with a size of between 1 to 10 microns and containing a polymeric shell comprising a copolymer with a glass transition temperature of at least 40.degree. C., see the Abstract of the Disclosure, for example; and U.S. Pat. No. 4,762,752 which discloses addition compounds suitable as dispersing agents, reference the Abstract of the Disclosure, for example.
Additionally, there is illustrated in U.S. Pat. No. 4,565,764 a pressure fixable microcapsule toner having a colored core material coated successively with a first resin wall and a second resin wall. The first resin wall has affinity to both the core material and the second resin wall. This patent discloses that the first resin wall may be of a material that becomes charged to a polarity opposite to that of the second resin wall and the core material.
Furthermore, U.S. Pat. No. 4,520,091 discloses a pressure fixable encapsulated electrostatographic toner material. The core comprises a colorant, a polymer, a solvent capable of dissolving the polymer or causing the polymer to swell, and an organic liquid incapable of dissolving the polymer or causing the polymer to swell, and the shell may consist of a polyamide resin. Preparation of the toner material is completed by interfacial polymerization.
Another patent, U.S. Pat. No. 4,708,924, discloses a pressure fixable microcapsule type toner composed of a core material and an outer wall over the core material. The core material contains at least a combination of a substance having a glass transition point within the range of -90.degree. C. to 5.degree. C. with a substance having a softening point within the range of 25.degree. C. to 180.degree. C. This toner composition may comprise substances such as polystyrene and poly(n-butyl)methacrylate and their copolymers.
Further, U.S. Pat. No. 4,254,201 discloses a pressure sensitive adhesive toner consisting essentially of porous aggregates. Each aggregate consists essentially of a cluster of a multiplicity of individual granules of pressure sensitive adhesive substance, each granule being encapsulated by a coating film of a film-forming material. Particles of an inorganic or organic pigment and/or a magnetic substance are contained within the aggregate in the interstices between the granules and deposited on the surfaces of the encapsulated granules. The adhesive substance is selected from a copolymer of at least one monomer and as many as three other monomers.
In addition, U.S. Pat. No. 4,702,988 discloses a process for the preparation of encapsulated toner. A monomer composition and a colorant are dispersed in a liquid dispersion medium in the presence of a solid fine powdery dispersion stabilizer. The liquid is pressurized and then ejected into a low pressure section to form particles of monomer composition. These particles are then subjected to suspension polymerization to produce toner particles.
In U.S. Pat. No. 4,727,011 there is disclosed a process for preparing encapsulated toner compositions which comprises mixing, in the absence of a solvent, a core monomer, an initiator, pigment particles, a first shell monomer, stabilizer, and water; thereafter adding a second shell monomer, thereby enabling an interfacial polymerization reaction between the first and second shell monomers; and subsequently effecting a free radical polymerization of the core monomer. The disclosure of this patent is totally incorporated herein by reference.
Moreover, U.S. Pat. No. 4,766,051, the disclosure of which is totally incorporated herein by reference, illustrates an electrophotographic developer composition comprising a cold pressure fixable colored toner composition which comprises a core containing a polymer in which is dispersed pigment particles selected from the group consisting of cyan, magenta, red, yellow pigments, and mixtures thereof, other than carbon blacks and magnetites; and encapsulated within a polymeric shell formulated by an interfacial polymerization. Also, U.S. Pat. No. 4,725,522 discloses a process for preparing cold pressure fixable toner compositions which comprises admixing a core component comprising pigment particles, a water insoluble organic solvent and elastomeric materials with a shell monomer dissolved therein, and dispersing the resulting mixture in a water phase.
In U.S. Pat. No. 4,563,212, the disclosure of which is totally incorporated herein by reference, Becher et al., describes a microencapsulation procedure based upon an interfacial polymerization reaction wherein the material to be encapsulated is an agricultural chemical such as an herbicide, an insecticide, a plant growth regulator or a herbicidal antidote. Becher et al., discloses a process wherein a water immiscible material containing the first shell wall component is emulsified into an aqueous solution containing an emulsifier selected from the group consisting of sulfonated naphthalene formaldehyde condensates, sulfonated polystyrenes and functionalized oligomers. In Becher et al., an oil-in-water emulsion is formed with the aid of high shear; the second shell wall component is added to the oil-in-water emulsion; and after a short period of time, the shear rate is reduced. Shear is continued for varying periods of time, following which salt is added to the suspension to balance its density. The formulation is subsequently bottled.
Further U.S. Pat. No. 4,785,048, the disclosure of which is totally incorporated herein by reference, discloses a process for the production of microcapsule slurry suitable for use in carbonless copy paper coatings and applications which provide microcapsules with signficant increases in capsule wall impermeability and strength. The disclosed process involves formation of microcapsule walls by hydrogen transfer polymerization in the presence of an aqueous mixture of partially hydrolyzed poly vinyl alcohol (PVA) and naphthalene-sulfonic acid formaldehyde (NSF) condensate or diphenyloxide disulfonate (DDS).
There are disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there are disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there is disclosed in the prior art encapsulated toner compositions containing pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
There is illustrated in U.S. Pat. No. 4,937,167, the disclosure of which is totally incorporated herein by reference, a process for controlling the electrical characteristics of colored toner particles. The process comprises preparing a first core material comprising first pigment particles, core monomers, a free radical initiator, and optional polymer components, second pigment particles being of a different color from that of the first pigment particles; encapsulating separately the first core material and the second core material within polymeric shells by means of interfacial polymerization reactions between at least two shell monomers, of which at least one is soluble in aqueous media and at least one of which is soluble in organic media, wherein the polymeric shell encapsulating the first core material is of substantially the same composition as the polymeric shell encapsulating the second core material; and subsequently polymerizing the first and second core monomers via free radical polymerization, thereby enabling, for example, two encapsulated heat fusible toner compositions of different colors with similar triboelectric charging characteristics.
Illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in application U.S. Ser. No. 718,676, (now abandoned) the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process.
Application U.S. Ser. No. 043,265/87, (now abandoned) the disclosure of which is totally incorporated herein by reference, illustrates an encapsulated composition suitable for use as an electrophotographic toner, which comprises a core encapsulated within a thermotropic liquid crystalline polymeric shell. On page 8 of this application, the specification indicates that the disclosed developer compositions can be charged to preselected values irrespective of the pigment selected for the core. In addition, U.S. Pat. No. 4,855,209, the disclosure of which is totally incorporated herein by reference, illustrates an encapsulated toner composition with a melting temperature of from about 65.degree. C. to about 140.degree. C. which comprises a core containing a polymer selected from the group consisting of polyethylene succinate, polyhalogenated olefins, poly(.alpha.-alkylstyrenes), rosin modified maleic resins, aliphatic hydrocarbon resins, poly(.epsilon.-caprolactones), and mixtures thereof; and pigment particles, where the core is encapsulated in a shell prepared by interfacial polymerization reactions.
Further, U.S. Pat. No. 4,851,318, the disclosure of which is totally incorporated herein by reference, illustrates an improved process for preparing encapsulated toner compositions which comprises mixing core monomers, an initiator, pigment particles, and oil soluble shell monomers, homgenizing the mixture into an aqueous surfactant solution to result in an oil-in-water suspension enabling an interfacial polymerization reaction between the oil soluble and the water soluble shell monomers, subsequently adding a low molecular weight polyethylene oxide surfactant protective colloid, and thereafter effecting free-radical polymerization of the core monomers by heating.
Free-radical polymerization is well known, and can be generalized as bulk, solution, or suspension polymerization. These polymerizations are commonly used for the manufacture of certain polymers. The kinetics and mechanisms for free-radical polymerization of monomer(s) is also well known. In these processes the control of polymer properties such as molecular weight and molecular weight dispersity can be effected by initiator, species concentrations, temperatures, and temperature profiles. Similarly, conversion of monomer is effected by the above variables.
Accordingly, there is a need for encapsulated toner compositions with many of the advantages illustrated herein. More specifically, there is a need for encapsulated toners wherein toner particle agglomeration is eliminated or minimized. Also, a need continues to exist for improved particle stabilization during free radical polymerization of heat fusible color toners suitable for use in electrophotographic copiers and printers. A need also exists for the stabilization of colored toners which exhibit low melting characteristics preferably with a low melting core Tg of less than about 55.degree. C., and a low melting polymeric shell Tg of less than about 100.degree. C. without particle agglomeration or coalescence during free radical polymerization thereby enabling lower fusing temperatures. A further need exists for dry colored toners with an average mean diameter of from about 5 microns to about 15 microns and a narrow geometric size distribution of less than 1.5 while avoiding micronization or classification. There is also a need for colored toner particles with clean, dirt free surfaces which aid in narrowing the size distribution (reduction of fines to, for example, less than 1 micron) and narrow the triboelectric charging distribution of the developer. Additionally, there is a need for an improved process for decreasing and/or eliminating the generation of fine particles. Also, there is a need for encapsulated colored toners wherein a minimum amount of surfactant or emulsifier is selected to generate toner size particles. There is a further need for encapsulated toners that will decrease or eliminate the grafting or incorporation of components such as poly(vinylalcohol) into the shell at elevated temperatures. Also, there is a need for encapsulated colored toners with a higher loading of organic phase in an aqueous phase. Moreover, there is a need for encapsulated toners wherein images with excellent resolution and no background development are obtained. Additionally, there is a need for encapsulated toners, including colored toners wherein the amount of emulsifier selected can be reduced. These and other needs are obtained with the encapsulated toner compositions of the present invention and the processes thereof.